Re: [PATCH] mailbox: cancel timer before starting it

[Kevin Hilman]

Jerome Brunet <jbrunet@xxxxxxxxxxxx> writes:

> If the txdone is done by polling, it is possible for msg_submit() to start
> the timer while txdone_hrtimer() callback is running. If the timer needs
> recheduling, it could already be enqueued by the time hrtimer_forward_now()
> is called, leading hrtimer to loudly complain.
>
> WARNING: CPU: 3 PID: 74 at kernel/time/hrtimer.c:932 hrtimer_forward+0xc4/0x110
> CPU: 3 PID: 74 Comm: kworker/u8:1 Not tainted 5.9.0-rc2-00236-gd3520067d01c-dirty #5
> Hardware name: Libre Computer AML-S805X-AC (DT)
> Workqueue: events_freezable_power_ thermal_zone_device_check
> pstate: 20000085 (nzCv daIf -PAN -UAO BTYPE=--)
> pc : hrtimer_forward+0xc4/0x110
> lr : txdone_hrtimer+0xf8/0x118
> [...]
>
> Canceling the timer before starting it ensure that the timer callback is
> not running when the timer is started, solving this race condition.
>
> Fixes: 0cc67945ea59 ("mailbox: switch to hrtimer for tx_complete polling")
> Reported-by: Da Xue <da@libre.computer>
> Signed-off-by: Jerome Brunet <jbrunet@xxxxxxxxxxxx>

Reviewed-by: Kevin Hilman <khilman@xxxxxxxxxxxx>

Kevin